1. Field of the Invention
The present invention relates to a resist composition and a resist pattern forming method.
2. Background Art
In lithography techniques, for example, a process including forming a resist film formed of a resist material on a substrate, performing selective exposure on the resist film, and performing a development treatment, thereby forming a resist pattern having a predetermined shape on the resist film is performed. A resist material whose characteristics are changed so that the exposed areas of the resist film are dissolved in a developing solution is referred to as a positive type, and a resist material whose characteristics are changed so that the exposed areas are not dissolved in a developing solution is referred to as a negative type.
In recent years, in the manufacturing of semiconductor elements and liquid crystal display elements, advances in lithography technologies have led to rapid progress in the field of pattern miniaturization. In general, these miniaturization techniques involve shortening of the wavelength (increasing the energy) of the exposure light source. Specifically, ultraviolet rays represented by g-line or i-line have hitherto been used. But nowadays, KrF excimer lasers and ArF excimer lasers are starting to be introduced in mass production of semiconductors. In addition, investigations are also being conducted on EUV (extreme ultraviolet radiation), EB (electron beams), X-rays, and the like, which have a shorter wavelength (higher energy) than these excimer lasers.
The resist material is required to have lithography properties such as sensitivity to the exposure light source and resolution capable of reproducing patterns of minute dimensions.
As the resist material that satisfies such requirements, a chemically amplified resist composition containing a base material component which exhibits changed solubility in a developing solution by the action of an acid and an acid generator component that generates an acid upon exposure has been used.
For example, in the case where the developing solution is an alkali developing solution (alkali development process), a composition containing a resin component (base resin) exhibiting increased solubility in the alkali developing solution by the action of an acid and an acid generator component is generally used as a positive-type chemically amplified resist composition. When a resist film formed using such a resist composition is selectively exposed during the formation of a resist pattern, an acid is generated from the acid generator component in the exposed areas, the polarity of the base resin increases by the action of the acid, and thus the exposed areas become soluble in the alkali developing solution. Therefore, alkali development is performed to form a positive type pattern in which the unexposed areas remain as a pattern.
When such a chemically amplified resist composition is applied to a solvent development process using a developing solution (organic developing solution) containing an organic solvent, the solubility in an organic developing solution relatively decreases as the polarity of the base resin increases. Thus, the unexposed areas of the resist film are dissolved and removed by the organic developing solution and a negative type resist pattern in which the exposed areas remain as a pattern is formed. The solvent development process adapted to form a negative type resist pattern as described above is sometimes referred to as a negative type development process (see, for example, JP-A-2009-025723).
In general, the base resin used in the chemically amplified resist composition has plural kinds of constituent units for the purpose of enhancing lithography properties and the like.
For example, in the case of a resin component which exhibits increased solubility in an alkali developing solution by the action of an acid, a constituent unit including an acid decomposable group which is decomposed by the action of an acid generated from an acid generator to increase its polarity is used. In addition, a constituent unit including a lactone-containing cyclic group, a constituent unit including a polar group such as a hydroxyl group, and the like are used in combination (see, for example, JP-A-2003-241365).
Recently, a demand for a high-molecular weight compound which is useful as a base resin for a resist composition has increased with gradual progress in the field of pattern miniaturization.
For example, in order to improve roughness, a resist composition using a high-molecular weight compound having a constituent unit including a monocyclic group-containing acid decomposable group as the above-described acid decomposable group is proposed (see JP-A-2008-003381).